A Health Maintenance Organization (HMO) is a type of Managed Care Organization (MCO) that provides a shape of health insurance coverage in the United States that is satisfied through hospitals, doctors, and other providers with which the HMO has a contract. Unlike traditional indemnity insurance, care provided in an HMO usually follows a set of care guidelines provided through the HMO's network of providers. Under this model, providers agreement with an HMO to obtain more patients and in return typically agree to provide services at a discount. This agreement allows the HMO to accuse a lower monthly premium, which is an advantage over indemnity insurance, provided that its members are eager to abide by the additional restrictions.

In addition to using their contracts with providers for services at a inferior price, HMOs hope to gain an benefit over traditional insurance plans by managing their patients' health care and reducing unnecessary services. To attain this, most HMOs require members to select a main care physician (PCP), a doctor who acts as a "gatekeeper" to medical services. PCPs are typically internists, pediatricians, family doctors, or general practitioners. In a characteristic HMO, most medical needs must first go through the PCP, who authorizes referrals to specialists or additional doctors if deemed necessary. Emergency medical care does not require previous authorization from a PCP, and many plans permit women to select an OB/GYN in addition to a PCP, whom they may see without a referral. In some cases, a constantly ill patient may be allowed to select a specialist in the field of their sickness as a PCP.

HMOs often have a negative public image due to their warning appearance. HMOs have been the goal of lawsuits claiming that the restrictions of the HMO prevented necessary care. Whether an HMO can be held liable for a physician's negligence partially depends on the HMO's screening process. If an HMO only contracts with providers meeting positive quality criteria and advertises this to its members, a court may be more likely to find that the HMO is liable, just as hospitals can be liable for negligence in selecting physicians. Since the HMO controls only the financial feature of providing care, not the medical feature, it is often insulated from malpractice lawsuits. The Employee Retirement Income Security Act (ERISA) can be detained to preempt negligence claims as well. In this case, the deciding issue is whether the harm results from the plan's management or the provider's actions.